Implementing customized PCB via creation through use of magnetic pads

ABSTRACT

A method and apparatus are provided for implementing customized printed circuit board (PCB) via creation through use of magnetic capture pads. At least one magnetic capture pad is rendered before aqueous seed and plate processing in the PCB manufacture. The magnetic capture pad selectively provides seed material rendering copper in at least one selected region of the via.

FIELD OF THE INVENTION

The present invention relates generally to the data processing field,and more particularly, relates to a method and apparatus forimplementing customized printed circuit board (PCB) via creation throughuse of magnetic pads.

DESCRIPTION OF THE RELATED ART

In today's complex high speed card and board designs; the electricalcharacteristics necessary for high speed interfaces do not tolerate thetypical electrical stub associated with through vias. These via stubs orremnants of the via not directly carrying through signals creatediscontinuities which can significantly degrade communications.

To combat this loss, designers require the removal of extraneous stubstypically through post card manufacturing mechanical drilling orchemical etching. Further, the mechanical processes are still prone toimperfections, remnants of metal not fully removed, drill wander, andstress induced defects.

While there are known processes to mechanically remove these stubs, onceback-drilled, it is no longer possible to probe those locations on theprinted circuit board (PCB), cost of the PCB increases substantially,and success of the process is statistically less than ideal. These factssignificantly complicate our ability to manufacture cost-effective PCBs,measure high-speed interfaces in the lab during system bring-up andmodel-to-hardware correlation activities, and maximize the electricalperformance of our computer interfaces. When system errors occur in thefield, the field engineer cannot measure and confirm function at thesePCB via locations while at the customer's site.

A need exists for a method and apparatus for implementing customizedprinted circuit board (PCB) via creation through use of magnetic pads,eliminating the need to back-drill, reducing PCB cost, and maximizinginterface margin.

As used in the following description and claims, the term printedcircuit board (PCB) should be understood to broadly include a printedwiring board or other substrate, an interconnect substrate, and varioussubstrates including a plurality of insulator layers, and internalconductive traces.

SUMMARY OF THE INVENTION

Principal aspects of the present invention are to provide a method andapparatus for implementing customized printed circuit board (PCB) viacreation through use of magnetic pads, eliminating post-cardmanufacturing processes. Other important aspects of the presentinvention are to provide such method and apparatus substantially withoutnegative effects and that overcome many of the disadvantages of priorart arrangements.

In brief, a method and apparatus for implementing customized printedcircuit board (PCB) via creation through use of magnetic pads. At leastone magnetic pad is rendered within the via before aqueous seed andplate processing in the PCB manufacture. The magnetic pad enableselectively rendering copper in at least one selected region of the via.

In accordance with features of the invention, the magnetic pads arerendered by an inner-layer PCB or flex processing step and can beaccomplished using conventional PCB manufacture methods.

In accordance with features of the invention, the magnetic padsoptionally hold ferrous seed material. The ferrous seed materialprohibits the seed layer from forming in the via barrel outside ofintended area with the seed material being captive by the aqueousmagnetic material, and is not be present in substantial quantity outsideof these specialized magnetic pad regions. As a result, the platingprocess renders copper only in the region captive by the magneticcapture pads.

In accordance with features of the invention, the magnetic padoptionally is a magnetic anti-pad holding ferrous resist material. Themagnetic pad ferrous resist material prohibits the seed layer fromforming in the via barrel outside the intended area of the magneticanti-pad.

In accordance with features of the invention, the methods of theinvention eliminate post-card manufacturing processes and allows thecard to be built as required without the issues and steps associatedwith mechanical/chemical steps.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention together with the above and other objects andadvantages may best be understood from the following detaileddescription of the preferred embodiments of the invention illustrated inthe drawings, wherein:

FIGS. 1A and 1B illustrates example structures for manufacturing aprinted circuit board (PCB) with enhanced via creation in accordancewith a preferred embodiment;

FIGS. 2A and 2B illustrates other example structures for manufacturing aprinted circuit board (PCB) with enhanced via creation in accordancewith a preferred embodiment;

FIG. 3 is a flow chart illustrating other example steps for implementingenhanced via creation in accordance with a preferred embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following detailed description of embodiments of the invention,reference is made to the accompanying drawings, which illustrate exampleembodiments by which the invention may be practiced. It is to beunderstood that other embodiments may be utilized and structural changesmay be made without departing from the scope of the invention.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

In accordance with features of the invention, a method and apparatus forimplementing customized printed circuit board (PCB) via creation throughuse of magnetic pads. At least one magnetic pad is rendered within thevia before aqueous seed and plate processing in the PCB manufacture. Themagnetic pad enables selectively rendering copper substantially only ina selected region of the via.

Having reference now to the drawings, in FIGS. 1A and 1B, there is shownexample structures generally designated by reference character 100 formanufacturing a printed circuit board (PCB) with enhanced via creationin accordance with the preferred embodiment.

In accordance with features of the invention, magnetic pads 124 of FIGS.1A and 1B and magnetic pads 224 of FIGS. 2A and 2B are rendered by aninner-layer PCB or flex processing step and can be accomplished usingone of several existing PCB manufacture methods.

Structure 100 includes a printed circuit board (PCB) 102 including aplurality of layers 112, 114, 116, 118, 120, 122, and 128, as shown. PCBincludes a plurality of magnetic pads 124 rendered within a via 126. PCB102 includes, for example, a plurality of insulator layers 112, 116,120, 128 with a plurality of conductive layers 114, 118, 122.

In accordance with features of the invention, the printed circuit board(PCB) 102 and via 126 are formed generally including conventional PCBmanufacturing processes, including via drilling.

Structure 100 includes a plurality of magnetic pads 124 rendered withinvia 126 and the PCB 102 before aqueous seed and plate processing in thePCB manufacture. Magnetic pads 124 advantageously eliminate via barrelstub creation during PCB plating processes during PCB manufacturing.

The magnetic pads 124 hold ferrous seed material. The ferrous seedmaterial prohibits the seed layer from forming in the via barrel outsideof intended area with the seed material being captive by the aqueousmagnetic material, and is not be present in substantial quantity outsideof these specialized capture pad regions. As a result, the platingprocess renders copper only in the region captive by the magnetic pads.The magnetic pads 124 present an inexpensive and quick method ofimproving signal performance OF the PCB 102 while also reducing theamount of electroplating required.

An effective adhesion promoter for magnetic pads 124 is a thin titaniumfilm, and for example, chromium is also be very beneficial on the seedlayer. If required, this additional adhesion film can be removed afterdevelopment of the resist where the structures are cleared. In thiscase, care must be taken not to under-etch the metallic adhesion layerunder the resist film. Therefore, the etching step should not take muchlonger than required for removing the uncovered metal film. Chromium isremarkable for its magnetic properties: it is the only elemental solidwhich shows antiferromagnetic ordering at room temperature and below.Above 38° C., chromium transforms into a paramagnetic state.

The magnetic pads 124 prevent the PCB plating process from creating viabarrel stubs, thus eliminating the need for post-processing steps, suchas mechanical drilling and chemical etching to improve cost andreliability of boards.

In accordance with features of the invention, the PCB plating processoptionally is performed using a generally conventional plating process.Conventional PCB finishing processes are performed while eliminating theneed to backdrill each via after the plating process by the use ofmagnetic pads 124.

U.S. Pat. No. 8,262,894 to Xu et al. issued Sep. 11, 2012 discloses amethod of changing a copper concentration in an electroplating bath,comprising: placing a substrate in a copper electroplating bathcomprising an acidic, aqueous solution exhibiting a copper ionconcentration; disposing a copper salt in solid form within a containerlocated in the copper electroplating bath, a chamber of the containerbeing in fluid communication with an the aqueous solution of the copperelectroplating bath; dissolving at least some of the copper salt insolid form to raise the copper ion concentration in the aqueous solutionand maintain the copper ion concentration in the aqueous solution atabout saturation to achieve high copper ion concentrations foraccommodating high speed plating; and electroplating copper on thesubstrate using a copper containing anode.

In accordance with features of the invention, a high speed aqueous seedand plate processing in the PCB manufacture can be used, such asdisclosed in the above-identified U.S. Pat. No. 8,262,894.

Referring to FIGS. 2A and 2B, there is shown example structuresgenerally designated by respective reference character 200, 230 formanufacturing a printed circuit board (PCB) with enhanced via creationin accordance with the preferred embodiment.

Structures 200, 230 include a printed circuit board (PCB) 202 includinga plurality of layers 212, 214, 216, 218, 220, 222, and 228, as shown.PCB includes a magnetic pad 224 rendered within a via 226. PCB 102includes, for example, a plurality of insulator layers 212, 216, 220,228 with a plurality of conductive layers 214, 218, 222. Structure 200includes the magnetic pad 224 rendered within via 226 and the PCB 202before aqueous seed and plate processing in the PCB manufacture.Magnetic pad 224 advantageously eliminates via barrel stub creationduring PCB plating processes during PCB manufacturing.

The magnetic pad 224 in structures 200, 230 holds a magnetic anti-padholding ferrous resist material. The magnetic pad ferrous resistmaterial prohibits a seed layer from forming in the via barrel outsidethe intended area of the magnetic anti-pad 224. A PCB aqueous seed andplate processing includes the plating process rendering copper 234substantially only in the region outside an intended area of themagnetic anti-pad as shown in FIG. 2B.

Referring now to FIG. 3, there is shown a flow chart illustratingexample steps generally designated by reference character 300 forreversal implementation of structures 100, 200 in accordance with thepreferred embodiment starting at a reversal implementation block 302.Doing so rejects either the ferrous material for structure 100 or theseeding material for structure 200, instead of containing suchmaterials. The end result is the same, yet reversal allows formanufacturing options.

The reversal implementations are carried out by: as indicated at a block304, reversing the polarity of the magnetic capture pads to rejectseeding capability beyond the intended layers.

As indicated at a block 306, polarity reversing is accomplished bylowering the PCB into the bath from a top layer or a bottom layer first.

As indicated at a block 308, lowering the PCB into the bath from oneedge is something which is performed by raw card and flex manufacturerstoday.

As indicated at a block 310, the reversed-polarity capture pad residesat the stop layer, opposite of the external surface which is beinglowered into the bath first.

In accordance with features of the invention, the alternative method forvia creation eliminates creation of the via barrel stub. Since the viabarrel stub is not created, the need for post-processing steps, such asmechanical drilling and chemical etching, are eliminated, reducing PCBcost and maximizing interface margin.

While the present invention has been described with reference to thedetails of the embodiments of the invention shown in the drawing, thesedetails are not intended to limit the scope of the invention as claimedin the appended claims.

What is claimed is:
 1. A structure for implementing enhanced viacreation without creating a via barrel stub during printed circuit board(PCB) manufacturing comprising: a printed circuit board (PCB); saidprinted circuit board (PCB) including a via; said via extending throughthe printed circuit board (PCB); a plurality of magnetic pads containedin said via including a plurality of magnetic capture pads; and platingcovering an intended area of the via only in a region captive by theplurality of magnetic capture pads, said plurality of magnetic padseliminating via barrel stub creation during PCB manufacturing.
 2. Thestructure as recited in claim 1 wherein said plurality of magnetic padsrendered by an inner-layer PCB processing step.
 3. The structure asrecited in claim 1 wherein said plurality of magnetic pads is formedwith ferrous seed material.
 4. The structure as recited in claim 3wherein said ferrous seed material prohibits a seed layer from formingin a via barrel outside of intended area with the seed material beingcaptive by an aqueous magnetic material.
 5. The structure as recited inclaim 1 wherein said plurality of magnetic pads includes at least onemagnetic anti-pad.
 6. The structure as recited in claim 5 wherein saidplurality of magnetic pads is formed with ferrous resist material.